Wood Bearing Perpendicular to Grain (NDS 3.10)
The crushing check a framer skips until the beam sinks into the plate: where a joist or beam lands across the grain, fc_perp = R/(b x lb) must clear Fc_perp x Cb, where the NDS 3.10.4 bearing-area factor Cb = (lb + 0.375)/lb rewards a short interior bearing. An 800 lb joist on 1.5 in of DF-L plate runs at DCR 0.46 and needs only 0.85 in; put a 6,000 lb beam reaction on the same footprint and it fails at 3.4x, demanding 6.4 in or a bearing plate. Fc_perp takes no load-duration factor. A design aid, not the engineer of record's stamped design.
Formula and source
Cb = (lb < 6 in and not within 3 in of the end) ? (lb + 0.375)/lb : 1.0; Fc_perp' = Fc_perp x Cb; fc_perp = R/(b lb); DCR = fc_perp / Fc_perp'; lb_req = R/(b Fc_perp) (Cb = 1, conservative).
The NDS 2018 3.10.2 compression-perpendicular-to-grain bearing check and the 3.10.4 bearing-area factor Cb = (lb + 0.375)/lb for a bearing under 6 in and not within 3 in of the member end, by name.
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